This invention relates to a construction and manner of forming thermoplastic pellets, including means for extruding strands of thermoplastic material substantially into an air or other gaseous environment enclosing chamber as contrasted to a liquid coolant submerged system. The strands are cut or broken into discrete particles or pellets by rotating knives, subsequently entrained in coolant flows and thereafter removed from further processing. The invention is particularly directed to a novel pellet cage construction for cooling and collecting such thermoplastic pellets and the manner in which such cooling is performed so as to reduce and/or prevent collision of such pellets prior to or during their cooling. Such action prevents the pellets from sticking together when hot to form multiple clusters thereof. Clusters are undesirable in later processing, such as conveying, weighing and feeding to subsequent extrusion operations.
A number of pellet cage designs are available, generally for the same purposes as above indicated, including that disclosed in U.S. Pat. No. 3,343,213 issued Sept. 26, 1967, which discloses the use of a cooling hood of substantially circular cross section in which pellets emerging from an adjacent extrusion die head are entrained in a single spiraling coolant flow. The pellets are progressively moved from their point of contact with the side walls of the hood forwardly therealong in such spiral motion to an exit at the forward end of the cage. The present applicants have found, however, that by eliminating the forward spiraling progression of such entrained pellets that the dwell time in which the pellets are present within the cage and the length of the cage itself can be substantially reduced and that highly effective cooling to prevent the above-referred-to cluster problem can be produced by the simultaneous provision of multiple coolant flows, one in a peripheral pattern about the inner walls of the cage, and the other in a radially outward pattern to cover the adjacent front face thereof. Newly formed pellets projected against either of such wall surfaces are accordingly immediately entrained in a coolant flow and are thereafter immediately upon completion of their arcuate travel about the periphery of the inner wall surfaces removed from the cage so as to not interfere with the effective cooling and removal of subsequent pellets.
It is accordingly an object of the present invention to provide a coolant cage of novel construction which enables thermoplastic pellets formed by extrusion and cutting means in operative association therewith to be cooled and removed therefrom in a minimum dwell time, yet assuring effective cooling so as to prevent formation of pellet clusters.
A further object of the present invention is the provision of a coolant cage for the receipt, cooling and minimum retention of thermoplastic pellets projected thereinto by an adjacent operatively associated thermoplastic strand extrusion and cutting means, wherein the pellets so projected initially contact either interconnected peripheral side or forward internal surfaces of such cage which cooperatively form a chamber for receipt of such pellets, which surfaces are both simultaneously provided with flows of liquid coolant thereover.
Still another object of the present invention is the provision of a coolant cage construction of the immediately aforementioned type, wherein means are provided for projecting a first coolant flow in a substantially single-path peripheral orbit about and in contact with a major portion of said internal side surfaces, whereby pellets entrained therein are immediately removed from such coolant cage without the necessity of forwardly advancing them along such side walls in a spiral attitude.
Another object of the present invention is the provision of a method of cooling thermoplastic pellets by their receipt and entrainment in one of a plurality of simultaneously provided fluid coolant flows provided about the side and front face internal surfaces of a coolant cage, and thereafter immediately withdrawing such entrained pellets so as to reduce the dwell time therein.
A still further object of the present invention is the provision of a novel slinger device which enables the front face of a coolant cage construction adapted for receipt of thermoplastic pellets emerging from an operatively associated thermoplastic extrusion and cutting means to be provided with an even flow of liquid coolant in an efficient manner with minimal power requirements.